In the prior art, a power storage device is mounted on a vehicle such as an EV (electric vehicle) or a PHV (plug in hybrid vehicle) to store power that is supplied to, for example, a motor. A power storage device may be, for example, a lithium-ion rechargeable battery or a nickel-metal hydride rechargeable battery. Patent document 1 discloses an example of a rechargeable battery that includes an electrode assembly, in which a positive electrode and a negative electrode have active material layers and are layered one over the other, and a cuboid case accommodating the electrode assembly. The case includes a rectangular box-shaped case body having a closed end and an opening, through which the electrode assembly is inserted, and a flat rectangular lid closing the opening of the case body. When the positive electrode and the negative electrode are stacked in a direction in which the short sides of the case extend, the electrode assembly is accommodated in the case. Additionally, tabs (non-applied portions) project from one side of each of the positive electrode and the negative electrode. The tabs are stacked to form tab groups (non-applied groups), each of which is joined to a conductive member having the corresponding polarity. Further, the conductive member is electrically connected to an electrode terminal having the corresponding polarity.
One method for assembling such a rechargeable battery integrates the electrode assembly and the lid with each other in advance. Then, after the electrode assembly is inserted into the case body, the lid is welded to the case body. To integrate the electrode assembly and the lid with each other, the positive electrode tab group and the negative electrode tab group are each connected to a conductive member having the corresponding polarity, and each of the conductive members is connected to an electrode terminal having the corresponding polarity. Subsequently, the electrode terminals are partially inserted through two through holes formed in the lid. Then, nuts are engaged with the electrode terminals projected from the lid to fasten the electrode terminals to the lid. Consequently, the electrode assembly, which is integrated with the electrode terminals by the conductive members, is also integrated with the lid.
A rechargeable battery is designed to increase the volume of the electrode assembly to a maximum extent so that the capacity is maximized. Thus, the electrode assembly is enlarged to the maximum extent in the depth-wise direction of the case so that the electrode assembly is located in the proximity of the inner bottom surface of the case body. The electrode assembly also has two end surfaces in the stacking direction of the positive electrode and the negative electrode. The electrode assembly is also enlarged to the maximum extent in a direction in which the short sides of the case extend so that the two end surfaces are located in the proximity of inner wall surfaces of the case.
When manufacturing a rechargeable battery, the electrode assembly is accommodated in the case with the lower surface of the electrode assembly located in the proximity of the inner surface of the bottom wall of the case. However, the end surfaces of the electrode assembly are separated from the inner wall surfaces of the case by small clearances. Thus, the electrode assembly needs to be forced into the case body so that the bottom surface of the electrode assembly is located in the proximity of the inner surface of the case. As described above, when the electrode assembly and the lid are integrated with each other in advance, the lid is pushed toward the electrode assembly to force the electrode assembly into the case body.
However, the impulse of pushing the electrode assembly together with the lid may result in damage to the bottom surface of the electrode assembly when colliding with the inner surface of the case body. Also, the electrode assembly is directly pushed by the lid. This may result in damage to the positive electrode and the negative electrode when colliding with the lid.